This invention relates to a fuel viscosity/density compensation device suitable for use with a fuel injection pump capable of supplying many types of fuel to an engine. More particularly this invention concerns the creation of an output signal for adjusting fuel flow based upon the viscosity of the fuel being utilized.
Certain internal combustion engines known as multi-fuel engines may be operated using a variety of fuels ranging from light fuels, such as gasoline, to heavy oils. Fuel injection pumps meter fuel into such engines on a volumetric basic without regard for the condition or thermal characteristics of the fuel. However, for a given throttle setting, the heat energy supplied to the engine and resulting power output may vary 20% or more depending upon the type of fuel used and the temperature and the viscosity of the fuel. Variations in fuel temperature cause changes in the density and consequently the thermal content of the fuel. More viscous fuels are also less subject to internal leakage in the injection pump. Hence, viscosity directly affects engine performance in several ways.
During operation of a multi-fuel engine at less than maximum power, compensation for changes in fuel conditions and characteristics may be made by adjustment of the throttle to maintain a desired engine output. Such compensation may be effected manually or by means of a govenor. However, at full load the throttle advance is limited by a full load stop which may have been manually set for each fuel used in accordance with the thermal capacity of the engine. Adjustment of the full load stop for each fuel employed is necessary to prevent overloading or to ensure the availability of maximum engine power. For example, if the full load stop were adjusted to provide rated engine output with diesel fuel, then if the engine were operated with gasoline, which has a lower heat content and is less viscous, the maximum output of the engine would drop substantially. On the other hand, if the full load stop were adjusted to provide rated output using gasoline as fuel, the engine could be overloaded and possibly damaged if operated with fuel oil.
Additionally it is not uncommon for the temperature of the fuel to change significantly under various operating conditions. The temperature of the fuel affects the density which also affects the volumetric amount of fuel available to the engine at the full load stop. Hence, any system for varying the volumetric amount of fuel supplied to the engine under full load conditions is likewise capable of adjusting for temperature conditions as well as changes in the fuel.
Previous attempts have been made to provide fluid density and viscosity control for use with fuel injected engines. In U.S. Pat. No. 3,215,185, there is disclosed adjusting the position of the full load stop by sensing the density of the fuel flow using a swirl-type orifice. U.S. Pat. Nos. 3,170,503, 3,204,623, 3,241,596, and 3,338,224 all disclose a fuel density compensating mechanism utilizing an annular orifice for sensing a pressure drop indicative of the viscosity of the fuel.
The operating principle of the device as disclosed in these patents is that with changes in the density or viscosity between fuels, a pressure difference is created which can be used to do useful work. A fluid motor is subjected to the pressure difference in order to change the position of the maximum fuel stop.
Each of the devices described in the above patents use only a single density/viscosity sensor. In the one series of patents, pressure is regulated to a constant value and then adjusted by means of a trimming valve and then discharged to a drain across the annular clearance formed by a housing bore in an operating piston. This annular clearance becomes viscosity sensitive as a function of the Reynolds number. With changes in density/viscosity the pressure drop across the annular clearance changes and provides a means of driving a fluid motor to regulate the position of the maximum fuel stop.
The device of the 3,215,185 patent utilizes a swirl-type orifice as the viscosity sensor. Again, the fluid pressure changes will change the density of the viscosity and its use to drive a fluid motor which, in turn, alters the position of the maximum fuel stop of the diesel fuel injection pump.
Both of the above devices have a basic fault. Neither device provides a sufficient pressure change as a function of the density/viscosity changes to adequately perform the required task of moving the maximum fuel stop to a new position. The force generated by the viscosity change in either device is marginal.
The principle described herein is the utilization of multiple staged devices in a particular manner to achieve significantly improved fluid pressure change as a function of the fluid density/viscosity variation.
In the herein described device, fluid under pressure enters a fuel inlet and is regulated at a constant pressure by the pressure regulator. The pressure level at the output on the pressure regulator serves to provide a desired pressure level at the bottom of the fluid motor piston which, along with the clearance dimension around the fluid motor piston, keep the Reynolds number of the fluid flow in the viscosity sensitive region.
The fluid then flows through an annular clearance between the fluid motor piston and the piston bore. The fluid pressure of the fluid discharge from the annular clearance to a serve chamber varies with the viscosity and density of the fluid. The fluid then exits the servo chamber across a needle valve and flows to drain pressure through a swirl orifice. The needle valve serves to trim or adjust the servo chamber pressure to the desired pressure for the fluid being used. The desired pressure is that pressure which places the vertical position of the maximum fuel stop at the correct length for the desired fuel
The combination of the annular flow clearance passage created by the piston to bore clearance and the swirl-type orifice is different than the previous devices. The annular flow orifice has a flow characteristic such that as the fluid density and viscosity decreases, the pressure drop across the piston decreases. The swirl-type orifice, on the other hand, has a diametrically opposite characteristic since as the fluid density and viscosity decrease, the pressure drop across the swirl orifice increases. Hence, the two viscosity sensitive elements of the device work together to more than double in some cases, the amount of servo pressure change as a function of the density viscosity change. The amount of change is determined by the Reynolds number for the annular flow passageway and all attendant passages. Also the swirl orifice velocity characteristic and Reynolds number can be adjusted for maximum effect by sizing of the tangential passages and discharge orifice length and diameters. By utilizing two sensing devices having diametrically opposing pressure drop characteristics, the compensation device has increased force resulting in improved displacement which results in increased stability and accuracy of the device.